Currently, a new time division duplex (Time Division Duplex, TDD) system is proposed, and the system is a half-contention and half-scheduling system. FIG. 1 is a structural diagram of a radio frame timeslot in a TDD system in the prior art. As shown in FIG. 1, a contention window (Contention Window, CW) and a scheduling window (Scheduling Window, SW) appear alternately. Because of uncertainty of a random contention manner, a CW period length dynamically changes and is unpredictable. However, an SW period length is predictable; each SW includes N radio frames (Radio Frame, RF), and there is a guard interval 1 (GAP1) between radio frames. Each radio frame includes a frame header (Header) and a digital field part. The digital field part includes two structures: a downlink period precedes an uplink period; and an uplink period precedes a downlink period (this scenario is not shown in the figure). In each structure, there are several downlink subframes in the downlink period, there are several uplink subframes in the uplink period, and there is a guard interval 2 (GAP2) between the uplink period and the downlink period. When data is transmitted in the TDD system, a sender device determines, according to feedback information, whether a receiver device correctly receives the data, so as to determine a next action. The feedback information includes an acknowledgement (Acknowledgement, ACK) and a negative acknowledgement (Negative Acknowledgement, NACK).
A radio frame with a data field part in which a downlink period precedes an uplink period is used as an example. In the prior art, transmission is performed after uplink data and downlink data are distinguished. For details, reference may be made to FIG. 2 and FIG. 3. FIG. 2 is a schematic diagram of downlink data transmission in the prior art; FIG. 3 is a schematic diagram of uplink data transmission in the prior art. As shown in FIG. 2, data 1 (DATA1) is sent in a downlink period of an nth radio frame, and the receiver device sends feedback information, for example, an ACK1, in an uplink period of the nth radio frame. In this process, the DATA1 and the ACK1 are completed within a same radio frame, and there is no problem with feedback information transmission. However, in FIG. 3, data DATA2 is sent in an uplink period of an nth radio frame, and the receiver device can send feedback information, for example, an ACK2, only in a downlink period of an (n+1)th radio frame. Likewise, data DATA3 is sent in the downlink period of the (n+1)th radio frame, and the receiver device needs to send feedback information, for example, an ACK3, only in a downlink period of an (n+2)th radio frame. Therefore, it can be learned that, for a radio frame in which a downlink period precedes an uplink period, when uplink data is transmitted, two radio frames need to be occupied to complete the uplink data and feedback information corresponding to the uplink data. In this way, for a last radio frame in a scheduling window, when sending any DATA in an uplink period, the sender device needs to wait for a CW with an unpredictable length before corresponding feedback information may be received. Consequently, a timeout occurs when the sender device is waiting for the feedback information, the sender device needs to resend the DATA in an uplink period or stops sending the data, and data transmission efficiency is low.
Likewise, when the data field part of the radio frame is of a structure in which an uplink period precedes a downlink period, for a last radio frame in a scheduling window, the sender device needs to wait for a CW with an unpredictable length before corresponding feedback information may be received. Consequently, a timeout occurs when the sender device is waiting for the feedback information, the sender device needs to resend the DATA in an uplink period or stops sending the data, and data transmission efficiency is low.